As semiconductor integrated circuits have become finer and more highly integrated, the steps involved in semiconductor manufacturing processes have increased in number and become more complicated. As a result, the surface state of a semiconductor device is no longer necessarily flat. The presence of steps on such surfaces leads to the breakage of wiring by steps, an increase in local resistance values, and the like, thus resulting in loss of wire connections, a drop in current capacity, and the like. Furthermore, this also leads to a deterioration in the withstand voltage and the occurrence of leaks in insulating films.
Meanwhile, as semiconductor integrated circuits have become finer and more highly integrated, the light source wavelength used in photolithography has become shorter, and the numerical aperture, or so-called NA, has become larger. Consequently, the focal depth of semiconductor exposure apparatuses has become substantially shallower. In order to handle such an increased shallowness of the focal depth, a flattening of device surfaces to a degree exceeding that seen in the past is required.
A technique known as chemical mechanical polishing or chemical mechanical planarization (hereafter abbreviated to “CMP”) has been widely used as a method for such flattening of the surfaces of semiconductor devices. Currently, this CMP technique is the only method capable of flattening the entire surface of a silicon wafer.
CMP was developed on the basis of a mirror surface polishing method for silicon wafers, and is performed using a CMP apparatus such as that shown in FIG. 18. 65 indicates a head part which applies rotation while holding a wafer 66 that constitutes the object of polishing. This head part 65 has a rotational driving mechanism 67. A rotating platen 69 to which a polishing pad 68 is bonded, and a rotational driving mechanism 70 for this rotating platen 69, are disposed facing this head part 65. The polishing pad 68, rotating platen 69 and rotational driving mechanism 70 are given a swinging motion by a rotating type swinging arm 71, and are driven upward and downward.
When polishing is performed using such a CMP polishing apparatus, the wafer 66 and polishing pad 68 are caused to rotate at a high speed, and the rotating type swinging arm 71 is lowered by a raising-and-lowering driving mechanism not shown in the figure, so that the wafer 66 is pressed by the polishing pad 68. Furthermore, a slurry constituting a polishing agent is supplied between the polishing pad 68 and wafer 66. Moreover, the rotating type swinging arm 71 is caused to swing as indicated by the broken line arrow by a swinging driving mechanism not shown in the figure. Consequently, as a result of the relative rotation and swinging of the polishing pad 68 and wafer 66, polishing of the wafer 66 is performed so that the surface of the wafer 66 is flattened. Specifically, favorable polishing is accomplished by a synergistic effect of mechanical polishing by the relative motion of the polishing pad 68 and wafer 66 and chemical polishing by the slurry.
In such a CMP polishing apparatus, the polishing pad 68 also becomes worn as the wafer 66 is polished. Accordingly, it is necessary to measure the surface shape and wear (reduction in thickness) of the polishing pad 68, and the reduction in the depth of the grooves formed in the polishing pad 68, and to perform polishing (dressing) of the polishing pad 68 itself, or to replace the polishing pad 68.
FIG. 19 shows the internal construction of the polishing chamber in a conventional CMP apparatus. A polishing station 42, a dressing station 43 and a pad replacement station 44 are disposed inside this polishing chamber 41.
The polishing pad 48 held on a rotating type swinging arm 46 is arranged so that this polishing pad 48 can be positioned on top of the polishing station 42, dressing station 43, pad replacement station 44, and the like by the rotation of the rotating type swinging arm 46.
When a specified number of wafer polishing passes has been completed, the rotating type swinging arm 46 shifts the polishing pad 48 from the polishing station 42 to the dressing station 43, and dressing of the polishing pad 48 is performed. After dressing is completed, the polishing pad 48 is removed, and the shape is measured by a measuring device not shown in the figure; then, the polishing pad 48 is again attached to the rotating platen, and if the measurement results are favorable, the polishing pad 48 is used “as is” in polishing. In cases where the shape is not favorable, dressing is performed again. Thus, conventionally, there has been no means for observing the surface of the polishing pad inside the CMP apparatus, so that the shape is measured after first temporarily removing the polishing pad from the polishing chamber.
However, removing the polishing pad from the rotating type swinging arm every time that the shape of the polishing pad is to be measured requires the expenditure of considerable effort; consequently, not only is the throughput lowered, but when he polishing pad is again mounted on the rotating platen, the mounted state differs from that prior to the removal of the polishing pad. As a result, distortion is newly generated, so that the flatness deteriorates, and there may be cases in which the desired polishing cannot be performed.